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Item Design and Fabrication of Micro-Channels and Numerical Analysis of Droplet Motion Near Microfluidic Return Bends(North Dakota State University, 2019) Singh, John-Luke BenjaminThree-dimensional spheroid arrays represent in vivo activity better than conventional 2D cell culturing. A high-throughput microfluidic chip may be capable of depositing cells into spheroid arrays, but it is difficult to regulate the path of individual cells for deposition. Droplets that encapsulate cells may aid in facilitating cell delivery and deposition in the return bend of a microfluidic chip. In this study, a low-cost method for fabricating polymer-cast microfluidic chips has been developed for rapid device prototyping. Computational fluid dynamic (CFD) simulations were conducted to quantify how a change in geometry or fluid properties affects the dynamics of a droplet. These simulations have shown that the deformation, velocity, and trajectory of a droplet are altered when varying the geometry and fluid properties of a multiphase microfluidic system. This quantitative data will be beneficial for the future design of a microfluidic chip for cell deposition into 3D spheroid arrays.Item Numerical Simulations of Electrohydrodynamic Evolution of Thin Polymer Films(North Dakota State University, 2015) Borglum, Joshua ChristopherRecently developed needleless electrospinning and electrolithography are two successful techniques that have been utilized extensively for low-cost, scalable, and continuous nano-fabrication. Rational understanding of the electrohydrodynamic principles underneath these nano-manufacturing methods is crucial to fabrication of continuous nanofibers and patterned thin films. This research project is to formulate robust, high-efficiency finite-difference Fourier spectral methods to simulate the electrohydrodynamic evolution of thin polymer films. Two thin-film models were considered and refined. The first was based on reduced lubrication theory; the second further took into account the effect of solvent drying and dewetting of the substrate. Fast Fourier Transform (FFT) based spectral method was integrated into the finite-difference algorithms for fast, accurately solving the governing nonlinear partial differential equations. The present methods have been used to examine the dependencies of the evolving surface features of the thin films upon the model parameters. The present study can be used for fast, controllable nanofabrication.Item Experimental Studies of Pulsatile Flow Passing Side Wall Biological Cavities and Flow Enhancement Using Hydrophobic Surfaces(2020) Eichholz, Benjamin KirkUnderstanding the hemodynamics of the cardiovascular system and associated diseases is important for mitigating health risks. We applied flow diagnostic techniques to investigate pulsatile flow characteristics past sidewall cavities, which have implications to two biomedical problems in the cardiovascular system: sidewall aneurysms and the left atrial appendage. Superhydrophobically-coated mesh diverters and synthetic slippery surfaces were studied for their effects on flow diversion and cavity flow enhancements. The study of pulsatile flow over a coated mesh diverter showed that the formation of the primary vortex was prevented which prevents flow stagnation and downwash flow in the cavity. The second study indicates that the healthy heart cycle is essential to reducing flow stasis inside the left atrial appendage. After applying a synthetic slippery surface to the interior of a side wall cavity model, this surface reduced the wall shear stress and allowed vortical flow to reach deeper into the cavity.Item Computational Investigation of Low-Pressure Turbine Aerodynamics(North Dakota State University, 2015) Flage, Alexander PaulThe design of today’s gas turbine engines is heavily reliant on accurate computational fluid flow models. Creating prototype designs is far more expensive than modeling the design on a computer; however, current turbulence and transitional flow models are not always accurate. Several turbulence and transition models were validated at North Dakota State University by analyzing the flow through a low pressure turbine of a gas turbine engine. Experimental data for these low pressure turbines was provided by the University of North Dakota. Two separate airfoil geometries are analyzed in this study. The first geometry is a first stage flow vane, and the second geometry is an incidence angle tolerant turbine blade. Pressure and heat transfer data were compared between computations and experiments on the turbine blade surfaces. Simulations were conducted with varying Reynolds numbers, Mach numbers, and free stream turbulence intensities and were then compared with experiments.Item Mechanical and Surface Properties of Technical and Single Flax Fiber in Micro and Nano Scale(North Dakota State University, 2017) Ahmed, ShabbirThe continued search for sustainable and eco-friendly materials led to the integration of bio-fibers as the reinforcement in composite materials. However, a wide variation in their mechanical properties poses a considerable challenge for their incorporation in load bearing and structural bio-composite materials. In this thesis, a rigorous experimental investigation is performed for quantifying this variation in mechanical properties of flax fiber such as ultimate strength, ultimate strain, and elastic modulus. The effect of stalk diameter and variety on strength and strain was investigated on a statistical basis. Probability distribution models were proposed for predicting the probability of failure on a given strength. A dynamic in-situ failure analysis was performed on technical flax fibers with the help of scanning electron microscopy (SEM) to investigate the micro and nanoscale failure behavior. A reliable measurement method of surface energy of a single flax fiber was proposed and performed by atomic force microscopy (AFM).Item Numerical Investigation of Vibration in a Steam Turbine Control Valve(North Dakota State University, 2017) Novak, Luke MichaelA numerical analysis is performed at North Dakota State University to investigate and resolve steam inlet control valve vibration in a Minnkota Power Cooperative turbine. Pressure fluctuations resulting from an unstable flow pattern are found to cause vibration. Multiple valve disc and seat design modifications to stabilize the flow are made and tested. The full scale geometry is used with steam as the working material. Both steady-state and transient analyses are completed. Analytical calculations are used for verification. Investigation of all modifications is discussed. Results from the original valve configuration show vortex shedding off of the disc. A currently installed cutoff disc has not removed flow-induced vibration. Flow expansion generates unstable flow, creating an unsteady separation bubble on the valve seat at the throat exit. Changing the throat from a converging-diverging to a purely converging nozzle stabilizes the flow, removing the flow-induced pressure forces causing disc vibration.Item Experimental Study of Effects of Leading-Edge Structures on the Dynamic Stall of a Vertical Axis Wind Turbine Airfoil(North Dakota State University, 2020) Zhao, JiamingVertical axis wind turbine, developed as one of the main methods to utilize the wind energy, has a promising future; however, the major issue to limit its performance is the uneven loading on the blade during operation. Flow control mechanisms have been employed in the aerodynamic field to improve the performance of airfoils. In this study, two types of leading-edge structures, including flexible leading-edge and leading-edge roughness, are experimentally investigated to analyze their effects on altering the aerodynamic characteristics of NACA 0018 airfoil under steady flow condition and dynamic pitching condition. Current experimental results indicate that 1) during the steady flow condition, both of leading-edge structures contribute to the delay of the static stall; 2) for the dynamic pitching process, the leading-edge structures either delayed the dynamic stall angle or increased the area of the coefficient of pressure loop as a function of angle of attack.Item Characterizing the Operation of a Dual-Fuel Diesel-Hydrogen Engine near the Knock Limit(North Dakota State University, 2014) Kersting, LeeA CAT C6.6 turbocharged diesel engine was operated in dual-fuel diesel-hydrogen mode. Hydrogen was inducted into the intake and replaced a portion of the diesel fuel. Hydrogen was added across multiple engine speeds and loads until reaching the knock limit, identified by a threshold on the rate of in-cylinder pressure rise. In-cylinder pressure and emissions data were recorded and compared to diesel-only operation. Up to 74% H2 substitution for diesel fuel was achieved. Hydrogen addition increased thermal efficiency up to 32.4%, increased peak in-cylinder pressure up to 40.0%, increased the maximum rate of pressure rise up to 281%, advanced injection timing up to 13.6°, increased NOx emissions up to 224%, and reduced CO2 emissions up to 47.6%. CO and HC emissions were not significantly affected during dual-fuel operation. At 25% load an operating condition was observed with low NOx and nearly 0 CO2 emissions, which however exhibited unstable combustion.Item A Survey for Industrial Uses of Distiller's Dried Grains with Solubles (DDGS)(North Dakota State University, 2012) Haugsdal, Joshua LouisThe increase in demand for corn ethanol has caused an increase in distiller’s dried grains with solubles (DDGS), which is a byproduct of ethanol production. DDGS is a cheap byproduct and is primarily used for livestock feed filler. DDGS contains oils and proteins from corn and in this research we showed that corn oil and proteins could be extracted with ethanol. Zein protein is the main protein in DDGS and has been shown to have good adhesive properties. This protein was used as a binder in biocomposites with the DDGS after extractions and soy protein isolate (SPI). Mechanical properties and water resistance of the composites were studied. A wood adhesive was also prepared using the zein and cellulose nano-fibrils (CNF) as the adhesive reinforcement. Rheological tests were performed to study the flow property of the adhesive. This research demonstrated the potential of DDGS to be used as a raw material for multiple value-added industrial uses.Item An Experimental Study on a Density Driven Solar Water Heating System Using Supercritical CO2 as Working Fluid(North Dakota State University, 2013) Shukla, RuchiFor supercritical carbon dioxide, a small change in temperature or pressure can result in large change in density, especially close to its critical point. At this pseudocritical region, density decreases rapidly with increase in temperature which aids the thermosyphon flow. Encouraged by this idea, an experimental investigation has been performed to investigate the feasibility and performance of thermosyphon solar water heating (SWH) system using R-744 (CO2) as the working fluid. Experimental results have shown that it is possible to induce the natural convective flow even during solar-adverse conditions. Although during winter this proposed density driven system was not possible to extract any useful heat gain, the system did show some promising results when operated during spring. The time-averaged collector and heat recovery efficiencies for summer were about 58% and 45%, respectively.